Optical transceivers used in an optical access market are broadly divided into a micro-optics modules including optical elements, such as a laser diode (LD) and a photodiode (PD), and optical components, such as a thin film filter and a lens; and a PLC (planer light-wave circuit) module configured by making a quartz waveguide on a silicon substrate and surface-mounting an optical element. Among them, methods of mounting an optical component, such as an optical element, in the PLC module include a passive alignment method as a mounting method without the need to adjust the optical axis.
In a passive alignment mounting, the position of an optical element in the planar direction with respect to an optical waveguide chip is determined by image detecting recognition of alignment markers provided on both using transparent, infrared light. The position in the vertical direction is determined by the height of a base block supporting the optical element. The height of the base block is accurately adjusted in the manufacturing process. Accordingly, an optical axis height with respect to the optical waveguide can accurately be adjusted by only mounting an optical component on the base.
JP2823044B (hereinafter, referred to as Patent Literature 1) discloses a related optical waveguide device. FIGS. 1A and 1B are perspective views showing optical waveguide device 100 described in Patent Literature 1. Optical waveguide device 100 includes optical waveguide 116 and optical element mount 117. Optical waveguide 116 includes waveguide formation layer 115 including lower clad layer 112, core layer 113 and upper clad layers 114a and 114b formed on silicon substrate 111. Optical element mount 117 is formed by removing a part of optical waveguide formation layer 115. An end face of optical waveguide 116 exposed by removing the part of optical waveguide formation layer 115 is optically coupled with light emitting element 118 mounted on optical element mount 117.
Optical element mount 117 includes base blocks 119 and alignment markers 120, on which light emitting element 118 is mounted. Optical coupling between light emitting element 118 and an end face of optical waveguide 117 requires alignment in height between active layer 121 of light emitting element 118 mounted on optical waveguide device 100 and core layer 113.
FIG. 2 is an enlarged sectional view of light emitting element 118 and base block 119. As shown in FIG. 2, in a case where the active layer depth of light emitting element 118 is d1, height h1 of base block 119 is adjusted so as to agree with the difference between the height from silicon substrate 111 to core layer 113 (optical axis height) and active layer depth d1 of light emitting element 118.
JP2002-111113A (hereinafter, referred to as Patent Literature 2) discloses an optical module that determines the height of an optical element mounted in a passive alignment manner by means of the height of bump 9 for tentative connection. The technique disclosed in Patent Literature 2 allows the optical element to be accurately mounted.